This invention relates to a system for cooling the airframe of a aircraft designed to fly in a cruise range of Mach 2 to Mach 8. The particular system to be described has been designed for a Mach 6 aircraft which has a bare aluminum airframe. The definition of the word "bare" is that the aircraft has no shielding by, for example, high temperature resistant metals.
It is contemplated that hypersonic vehicles, or vehicles designed to fly in the Mach 6 speed range, often termed hypersonic aircraft, will utilize hydrogen as an engine fuel. Since liquid hydrogen is extremely cold, various techniques have been proposed for utilizing the hydrogen fuel as a heat sink to cool the airframe of such an aircraft. Various techniques have been suggested for circulating either the hydrogen fuel or a coolant through various passages formed in the aircraft airframe and adjacent the skin thereof and extracting the heat which is being generated by the aircraft as it travels at such a high rate of speed. Systems to date have passed the coolant or fuel which has absorbed the heat through some type of heat exchanger which removes at least a portion of the heat from the fuel or coolant.
Prior art devices; however, have not been shown to have a design capability such that the entire heat generated by the aerodynamic heating of the aircraft airframe can be totally or adequately disposed of. As a result, the aircraft cooling procedure must include not only an active cooling system as discussed above, but also some type of shielding. Shielding involves the use of high temperature metal such as titanium or stainless steel, or possibly some of the composite structures which are now available. The use of shielding is obviously undesirable for many reasons. Initially, high temperature resistant structures are very expensive compared to aluminum which has been a standard structure for aircraft for many years. Further, the use of high temperature resistant shielding materials increases the mass of the aircraft while adding no strength thereby affecting the overall efficiency of the aircraft in every respect.
From the above discussion, it is apparent that it would be extremely desirable to cool a hypersonic aircraft to temperatures which an airframe constructed of aluminum could withstand. Aluminum is a structural material which is readily available in large quantities, as opposed to a high temperature material such as titanium. Aircraft constructed of aluminum have proven high structural efficiency, and known long life fabrication characteristics.
Accordingly, it is an object of this invention to provide a cooling system for a hypersonic aircraft which is constructed from bare aluminum (i.e., no shielding being utilized).
It is a further object of this invention to provide a cooling system wherein a coolant is passed through a closed loop having passages associated with the airframe for extracting heat from the airframe.
Another object of the invention is to remove essentially all of the heat from the coolant with heat exchanging mechanism and a heat pump.
Yet, another object of the invention is to provide a cooling system having a heat pump which has associated therewith one or more power turbines, the power turbines being driven by heat energy extracted from the cooling system.
Another object of the invention is to provide a cooling system wherein the power turbines forming a part thereof are utilized to drive aircraft subsystems such as pumps, electrical systems, hydraulic systems, and mechanical systems such as gear trains.
A prime object of the invention is to provide sufficient cooling to allow removal of the heat shields with no penalty in aircraft performance.
A further object of the invention is to provide a cooling system having power turbines wherein the power turbine is utilized to drive the heat pump compressor.
Another object of the invention is to provide a cooling system wherein the power turbines thereof are utilized to drive a booster fuel pump to raise the temperature and pressure of the fuel to a point such that efficient aircraft engine operation is obtainable.
A further object of the invention is to provide a cooling system wherein the aircraft fuel system is utilized as a heat sink, for cooling the aircraft engines.
Still another object of the invention is to provide an aircraft cooling system having a heat pump with alternating condenser stages and power extracting turbines utilized to reduce system weight and increase system efficiency.